At joint press conferences in New York and Chicago today, the Council on Tall Buildings and Urban Habitat—a Chicago-based nonprofit—announced its decision to crown the One World Trade Center as the tallest building in the United States,beating out the Windy City's Willis Tower by mere feet of spire.

Why did it take 25 officials and months of discussion to figure out what the country's tallest building is? It all comes down to the spire. Here's the core of the disagreement: The top floor of the Willis Tower—née the Sears Tower—sits at 1,345 feet. The top floor of One World Trade, meanwhile, sits at 1,268 feet, making Willis Tower the clear winner. But if you take spire height into account, it's One World Trade—by 63 feet.

The CTBUH's ruling is based on the details of what purpose the spire actually serves. They've long held that a spire must be "integral" to the building's design for it to count towards the total height—this definition excludes radio antennas, for example. "Even though the cladding was taken off the spire, you can still see that is is an architectural element," said one CTBUH official about the WTC spire, according to the Chicago Tribune. "It is not just a plain steel mast from which to hang antenna or satellite dishes."

The Chicago vs. New York debate cuts to the core of a new phenomenon in supertall construction called "vanity spire." Massive spires have increased by more than 400 percent since 1970, when the Willis Tower topped out in Chicago. What's the purpose of these huge steel columns? Not much, actually—hence the moniker. Yet architects and developers have raced to slap extra spire height onto buildings that could potentially clinch a title for height.

For example, without its vanity spire, Dubai's Burj Khalifa would be 700 feet shorter. For One World Trade, those extra spire feet are also a matter of reaching the symbolic (and overwrought) 1,776 feet goal laid out by the building's original architect, Daniel Libeskind. And it's not the only building in New York to tack on most of its height in the spire: The Bank of America Tower and the New York Times Tower, too, are some of the tallest spires in the world.

Image: Getty/Handout.

For supertall purists, spires seem like a shameful way for developers to keep pushing into the sky—without actually adding any useful construction innovations. After all, the architectural height of tall buildings hasn't changed much over the past three decades, while total height has skyrocketed. Today's decision is bound to rankle with people who think that a building should be measured by its tallest floor, not its tallest bit of metal.

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Though it's easy to be cynical about the media frenzy whipped up by the Council, you have to admit that it's sort of fun. The architectural rivalry between New York and Chicago is more than a century old. Its golden age came to a head in the 1890s, when the cities were pitted the cities against each other in a fight over who would host the 1893 World's Fair (Chicago won).

That rivalry dimmed out in the 20th century, and it's great to see it return—if only for a day.